A technology called flow cytometry is currently used for analysis of microparticles related to a field of living organisms such as cells and microorganisms. Flow cytometry is an analytical method of analyzing and sorting microparticles by radiating light to microparticles that flow to be contained in a sheath flow feeding a liquid in a flow path formed in a flow cell, a microchip, or the like and detecting fluorescence or scattered light emitted from the individual microparticles. A device used in such flow cytometry is called a flow cytometer (which may also be called a “cell sorter”).
In such a flow cytometer, a vibration element is generally provided in a part of a flow path in which microparticles contained in a sheath flow flow. Vibration is imparted by this vibration element to a part of the flow path, and a fluid discharged from a discharge port of the flow path is continuously made into droplets. In addition, the flow cytometer employs a configuration in which predetermined electric charge is applied to a droplet containing microparticles, a traveling direction of the droplet is changed by a deflecting plate or the like on the basis of the electric charge, and only target microparticles are collected in a predetermined place or the like of a predetermined container or plate.
For a flow cytometer, a technique of controlling stable droplet formation is an important factor for improving accuracy in analysis. Here, it is known that, if formation of a droplet is unstable, such as when a break-off (break-off) timing at which a fluid discharged from a discharge port of a flow path is made into a droplet is unstable, or the like, a time at which an electric charge is applied to the droplet becomes unstable as well, and as a result, sorting of microparticles becomes unstable. However, control of the formation of a droplet is difficult because a plurality of factors such as environmental conditions such as flow rate, temperature, and humidity, sizes of microparticles, and the like are involved therein.
With regard to this matter, for example, Patent Literature 1 discloses a technology for stabilizing break-off timings. In this technology, a magnitude of vibration is controlled in accordance with a distance from a break-off point to a first satellite.